Field
The present disclosure relates to a fingerprint sensor integrated type touch screen device and a method of driving the same, and more particularly to a touch screen device having a fingerprint recognition function.
Discussion of the Related Art
With the development of computer technology, computer based systems that can be applied to various utilities such as notebook computers, tablet personal computers (PCs), smart phones, personal digital assistants (PDAs), automated teller machines (ATMs), and information systems, have been developed. In general, computer based systems store various data including private information such as secret business information and personal information related to private affairs. Thus, strong security mechanisms are typically desired to protect such information.
To this end, fingerprint sensors have been developed to strengthen security by performing registration or certification of systems using fingerprints of human beings.
The fingerprint sensor is a sensor capable of sensing fingerprints of human beings. A fingerprint sensor can be classified into an optical fingerprint sensor and a capacitive fingerprint sensor.
The optical fingerprint sensor is based on the principle that a light source, such as a light emitting diode (LED), emits light and the light reflected from ridges and valleys of a fingerprint is sensed through a CMOS image sensor. Problems in this field concern an increase in size due to the use of LEDs and a rise in the product cost due to the use of expensive light source.
The capacitive fingerprint sensor utilizes a difference of electric charges charged between ridges and valleys of the fingerprint contacted thereto.
U.S. Patent Publication No. 2013/0307818 published on Nov. 21, 2013, and entitled “Capacitive Sensor Packaging” describes a capacitive fingerprint sensor of a related art. The published capacitive fingerprint sensor is configured as an assembly form coupled with a particular push button. The capacitive fingerprint sensor includes a silicon wafer on which a circuit for measuring a capacitance between a fingerprint (ridges and valleys) and a capacitive plate is printed.
In general, the capacitive fingerprint sensor described in US Patent Publication No. 2013/0307818 may need a high resolution sensor array and an integrated circuit (IC) for the fingerprint recognition processing because the fingerprint's ridges and valleys have a very minute size of about 300 μm to about 500 μm. To this end, the capacitive fingerprint sensor utilizes the silicon wafer for integrating the IC with the sensor array. However, when the IC and the high resolution sensor array are integrated using the silicon wafer, it is necessary for the capacitive fingerprint sensor to have an assembly configuration for coupling the fingerprint sensor with a push button. Thus, problems posed may include a complicated configuration and an increase in a non-display area (e.g., bezel area) of the optical fingerprint sensor due to the assembly configuration. Also, other problems may include the issue of increasing thickness and an area for sensing the fingerprint depends on the size of the push button (e.g., a home key of a smart phone) because the push button overlaps the fingerprint sensor.
To address the above-described problems, a technology has been developed to use an area of a touch sensor screen as a fingerprint recognition area. The technology is described in U.S. Pat. No. 8,564,314 issued on Oct. 22, 2013 and entitled “capacitive touch sensor for identifying a fingerprint” and Korean Patent No. 10-1432988 issued on Aug. 18, 2014 and entitled “fingerprint recognition integrated type capacitive touch screen”.
FIG. 1 schematically shows an arrangement of driving electrodes and sensing electrodes of a capacitive sensing panel shown in U.S. Pat. No. 8,564,314. FIG. 2 shows configuration of a fingerprint recognition integrated type capacitive touch screen shown in Korean Patent No. 10-1432988. FIG. 3A shows a general touch sensor pattern, and FIG. 3B shows a high-density sensor pattern.
Referring to FIG. 1, a capacitive touch sensor for identifying a fingerprint includes a touch sensor 3 including touch driving electrodes 1(x) and touch sensing electrodes 1(y) and a fingerprint sensor 5 including fingerprint driving electrodes 5(x) and fingerprint sensing electrodes 5(y). In the capacitive touch sensor for identifying the fingerprint, because the separate fingerprint sensor 5 is partially disposed on a screen area, problems posed may include a non-touch of the fingerprint sensor 5 or a reduction in a touch performance around the fingerprint sensor 5.
Referring to FIG. 2, a fingerprint recognition integrated type capacitive touch screen includes a touch panel AA, electrode connection lines BB, and a touch controller CC. The touch panel AA forms fine channels A3 through a combination of first channel electrodes A1 (one of Tx and Rx) and second channel electrodes A2 (the other of Tx and Rx) crossing each other. The fine channels A3 are configured such that the fine channels A3 of a remaining area except an area of fingerprint recognition sensors A4 from the fine channels A3 form a plurality of groups each serving as a touch group channel A5 for sensing a touch signal, and the fine channels A3 corresponding to the area of the fingerprint recognition sensors A4 each serve as a fingerprint recognition channel A6.
However, this fingerprint recognition integrated type capacitive touch screen may greatly increase a mutual capacitance Cm between touch channels because of the fine channels A3 (i.e., the touch channels) serving as the touch group channel A5. Namely, a mutual capacitance Cm between touch channels in a high-density sensor pattern shown in FIG. 3B may increase to several tens to several hundreds of times a general touch sensor pattern shown in FIG. 3A. Because an increase in the mutual capacitance Cm reduces sensitivity of the touch sensor, a touch operation may not be recognized when the touch operation is generated.